Artificial lighting, that is, light generated using an energy source, represents a major component of energy consumption, accounting for a significant part of all energy consumed worldwide. Artificial lighting is commonly provided by lighting devices using electricity as the energy source.
Conventional lighting technology includes the incandescent light bulb, also referred to as the incandescent lamp. The incandescent light bulb works by incandescence, that is, an electrical current passes through a thin filament, heating the filament until it produces light. An enclosing glass bulb prevents the oxygen in air from reaching the hot filament, which otherwise would be destroyed rapidly by oxidation. Incandescent bulbs are made in a wide range of sizes and voltages, from 1.5 volts to about 300 volts. Incandescent bulbs typically require no external regulating equipment and have a low manufacturing cost, and work well on either alternating current or direct current. As a result, the incandescent light bulb is widely used in household and commercial lighting, for portable lighting, such as table lamps, some car headlamps and electric flashlights, and for decorative and advertising lighting.
Incandescent light bulbs, however, use light emission resulting from resistance. Therefore, a large amount energy in an incandescent bulb is lost in the form of heat energy. Accordingly, the energy efficiency of incandescent light bulbs is relatively low. Incandescent light bulbs are gradually being replaced in conventional lighting technology by more efficient lamps including compact fluorescent lamps (CFLs), which give more visible light for the same amount of electrical energy input.
A CFL, also known as a compact fluorescent light bulb (or less commonly as a compact fluorescent tube (CFT)) is a type of gas discharge lamp. Many CFLs are designed to replace an incandescent lamp and include the standard base enabling the CFL to fit in existing light fixtures formerly used for incandescents.
Compared to incandescent lamps of the same luminous flux (i.e. luminous power), CFLs use less energy and have a longer rated life. For a given light output, CFLs use between one fifth and one quarter of the power of an equivalent incandescent lamp. A CFL can therefore significantly save electricity costs over the lamp's lifetime compared to an incandescent lamp. A CFL can also can save 2000 times its own weight in greenhouse gases due to its energy efficiency. While CFLs radiate a different light spectrum from that of incandescent lamps, improved phosphor formulations have improved the subjective color of the light emitted by CFLs such that some CFLs are subjectively similar in color to standard incandescent lamps.
As efficient as a CFL is over an incandescent lamp, the CFL also loses a significant amount of energy as heat energy. Fluorescent lamps pollute the environment when disposed of because of the toxic substances they typically contain. Further, the light intensity of gas discharge lamps tends to decrease over time with use. Additionally, gas discharge lamps typically produce ozone due to high voltage requirements and produce intense ultra-violet light that tends to cause the breakdown of many materials and may lead to gas leakage into the environment. Thus conventional lights have various problems.
Solid state lighting has been developed to overcome some of the problems of incandescent lamps and gas discharge lamps. Solid state lighting (SSL) refers to a type of lighting that utilizes light-emitting diodes (LEDs), organic light-emitting diodes (OLED), or polymer light-emitting diodes (PLED) as sources of illumination rather than electrical filaments or gas. The term “solid state” refers to the fact that light in an LED is emitted from a solid object—a block of semiconductor—rather than from a vacuum or gas tube, as is the case in traditional incandescent light bulbs and fluorescent lamps. The LED is a semiconductor diode that emits incoherent narrow-spectrum light when electrically biased in the forward direction of the p-n junction, as in the common LED circuit resulting in electroluminescence. Unlike incandescent or fluorescent lighting, however, SSL creates visible light with reduced heat generation or parasitic energy dissipation. In addition, its solid-state nature provides for greater resistance to shock, vibration, and wear, thereby increasing its lifespan significantly.
An LED is typically a small area source. The color of the emitted light depends on the composition and condition of the semiconducting material used, and can be infrared, visible, or near-ultraviolet. An LED provides direct light projection where incandescent lamps provide a fan-shape illumination pattern. The disadvantages of the LED are its narrower illuminating angle and difficulty in radiating light uniformly in all directions contrary to the conventional tungsten bulb. The angle of some LEDs has been improved by modifying the structure of the LED bulb.
Many conventional LED devices, however, are limited by thermal energy-management issues. For example, LEDs exhibit negative temperature coefficient aspects. That is, at a fixed power input, as the LED device's operating heat rises, the LED device's light output decreases. High heat during use can shorten the useful life of an LED. It is, however, desirable to run LEDs using high current, because the higher the current, the higher the brightness of the emitted light. Accordingly, there is motivation to manage heat as much as possible in order to operate an LED optimally with regard to power input and light output and LED life.
It remains desirable to have an LED illumination device wherein heat is managed such that lumens, energy consumption and lifespan are maximized.